Geometrical design of stand pipe air distributors for the combustion of municipal solid waste in a fluidised bed

The new geometrical design of stand-pipe air distributor for the combustion of the municipal solid waste was presented. The new design of the air distributors enables penetration of incombustible and unburnt carbon through opening between the air distributors, thus providing easy maintenance work. The fluidized bed experimental rig was constructed using Perspex column in which air was supplied through the distributors below it. In order to establish the final geometrical design of the air distributors, several design parameters were investigated. The effect of orifice size, distance between orifice and distance between distributor pipes on the fluidization behaviour were studied. Investigation on the effects of various orifice sizes of 1.5 mm, 2 mm, 3 mm, 4 mm and 5 mm showed that the 3 mm orifice size exhibited the most stable fluidization behaviour. Investigation on some selected orifice distances of 10 mm, 20 mm, 30 mm and 40 mm also found that the 10 mm orifice distance exhibited stable growths of bubbles. Various pipe distances of 30 mm, 40 mm, 50 mm, 60 mm and 70 mm were also investigated and the most suitable pipe distance was 70 mm

Measurement of PCDD/Fs emissions from a coal–fired power plant in Malaysia and establishment of emission factors

AbstractThis paper presents the PCDD/Fs emissions measured from a coal–fired power plant in Malaysia. The study discusses partitioning of PCDD/Fs in particle and gas phase, effects of coal quality to PCDD/Fs formation, effects of air pollution control device (APCD) configuration to PCDD/Fs formation and establishment of emission factors of PCDD/Fs from the studied coal–fired power plant. The results presented in this study were mostly in good agreement with the previous works on PCDD/Fs emissions conducted in other countries. Laboratory analysis results showed that PCDFs were the dominant congeners. The emissions of PCDD/Fs were low which most probably due to the high combustion efficiency. The PCDFs/PCDDs ratio was more than 1 and PCDD/Fs were detected in fly ash, hence speculating that the formation of PCDD/Fs during coal combustion was mainly through de novo synthesis. Analysis on partitioning of PCDD/Fs showed that the compounds were mainly emitted in gas phase. This study also indicated that type of coal influenced the formation of PCDD/Fs during coal combustion where bituminous coal with high sulfur (S) content resulted in slightly lower PCDD/Fs emissions compared to sub–bituminous coal. It was also found that operation of flue gas desulfurization (FGD) reduced the emission of PCDD/Fs. The established emission factors for PCDD/Fs were in the range of 0.08 to 0.11ng I–TEQ/kg

Study on freeboard temperature profile during combustion of rice husk in a fluidized bed combustor

In this paper, the temperature profile while firing rice husk in a fluidized bed combustor was investigated. The experiment was carried out in a 210 mm I.D. non insulated fluidized bed combustor with a height of 2000 mm. The experiments were carried out in two sets; firstly without any secondary burner and secondly with one and two secondary burners in the freeboard region and its effect on temperature was studied. The results without any secondary burner showed that the temperature reduces sharply along the height of the combustor with fluctuation in freeboard temperature. The reason was heat loss to surrounding due to non insulation of the fluidized bed combustor and run off flue gas . However, improvement or almost steady freeboard temperature profile was observed with addition of one and two secondary burners in the freeboard region. In addition to this, the high temperature (around 700°C) could help in burning off the carbon in the rice husk ash during elutriation from fluidized bed. Hence, freeboard region could be made as secondary combustion zone in obtaining high quality white siliceous ash

Combustion characteristics of refuse derived fuel (RDF) in a fluidized bed combustor

The combustion characteristics of refuse derived fuel (RDF) in a fluidized bed have been studied. The gross heating value (GHV) of the RDF was 14.43 MJ/kg with moisture content of 25% by weight. Parameters of interest for sustainable bed combustion were the fluidization number and primary air factor. The study was performed in a rectangular fluidized bed combustor with dimensions of 0.3 m in width, 0.7 m in length and 2 m in height. Sand with mean particle size of 0.34 mm was used as a fluidization medium. The sand bed height was at 0.3 m above the standpipes air distributor. The range of fluidization number under investigation was 5–7 Umf in which 5 Umf was found to be the optimum. The study was continued for the determination of the optimum primary air factor with the selected range of primary air factors being 0.6, 0.8, 1.0 and 1.2 in experiments conducted at 5 Umf. The final results showed that the optimum primary air factor was at 0.8. An energy balance was also performed to determine the thermal efficiency of the combustion. It was concluded that the thermal efficiency depended on the bed temperature and the primary air factor being used

Combustion of refuse derived fuel (RDF) in a fluidized bed combustor

The combustion characteristics of refuse derived fuel (RDF) in a fluidized bed have been studied. The gross heating value (GHV) of the RDF was 14.43 MJ/kg with moisture content of 25% by weight. Parameters of interest for sustainable bed combustion were the fluidization number and primary air factor. The study was performed in a rectangular fluidized bed combustor with dimensions of 0.3 m in width, 0.7 m in length and 2 m in height. Sand with mean particle size of 0.34 mm was used as a fluidization medium. The sand bed height was at 0.3 m above the standpipes air distributor. The range of fluidization number under investigation was 5-7 Umf in which 5 Umf was found to be the optimum. The study was continued for the determination of the optimum primary air factor with the selected range of primary air factors being 0.6, 0.8, 1.0 and 1.2 in experiments conducted at 5 Umf. The final results showed that the optimum primary air factor was at 0.8. An energy balance was also performed to determine the thermal efficiency of the combustion. It was concluded that the thermal efficiency depended on the bed temperature and the primary air factor being used

Understanding selected trace elements behaviour in a coal-fired power plant in malaysia for assessment of abatement technologies

The Proposed New Environmental Quality (Clean Air) Regulation 201X (Draft), which replaces the Malaysia Environmental Quality (Clean Air) 1978, specifies limits to additional pollutants from power generation using fossil fuel. The new pollutants include Hg, HCl, and HF with limits of 0.03, 100, and 15 mg/N-m3 at 6% O2, respectively. These pollutants are normally present in very small concentrations (known as trace elements [TEs]), and hence are often neglected in environmental air quality monitoring in Malaysia. Following the enactment of the new regulation, it is now imperative to understand the TEs behavior and to assess the capability of the existing abatement technologies to comply with the new emission limits. This paper presents the comparison of TEs behavior of the most volatile (Hg, Cl, F) and less volatile (As, Be, Cd, Cr, Ni, Se, Pb) elements in subbituminous and bituminous coal and coal combustion products (CCP) (i.e., fly ash and bottom ash) from separate firing of subbituminous and bituminous coal in a coal-fired power plant in Malaysia. The effect of air pollution control devices configuration in removal of TEs was also investigated to evaluate the effectiveness of abatement technologies used in the plant. This study showed that subbituminous and bituminous coals and their CCPs have different TEs behavior. It is speculated that ash content could be a factor for such diverse behavior. In addition, the type of coal and the concentrations of TEs in feed coal were to some extent influenced by the emission of TEs in flue gas. The electrostatic precipitator (ESP) and seawater flue gas desulfurization (FGD) used in the studied coal-fired power plant were found effective in removing TEs in particulate and vapor form, respectively, as well as complying with the new specified emission limits

Decision analysis of multi-pollutant control strategy for coal-fired power plant in Malaysia

The promulgation of Environmental Quality (Clean Air) Regulations 2014 on emissions from coal-fired power plants in Malaysia has prompted power plant operators to adopt emission control strategy that complies with the new emission limits. Currently, various emission control strategies are available to achieve the desired emission level. Each strategy offers unique advantages and disadvantages, depending on the objective of emissions control, process nature, and constraints on the resources incurred. To address this challenge, a proper decision-making analysis needs to be performed. In this paper, a systematic decision analysis methodology is proposed to select the most effective multi-pollutant control strategy that is compatible for coal-fired power plants in Malaysia. The methodology includes: (1) identification of pollutant emission from the plant under study and comparison with the stipulated emission limits, (2) establishment of emission factors, (3) selection of multi-pollutant control strategy, (4) identification of emission reduction factor for the pollutants and control technologies of interest, (5) determination of emission level from the selected multi-pollutant control strategy, and (6) prediction of ground-level concentration of pollutants. The decision analysis methodology is applied to a real case study of coal-fired power plant in Malaysia, which also currently faces a dilemma to comply with the additional and more stringent emission limits stipulated in the Environmental Quality (Clean Air) Regulations 2014. The proposed method is applicable for both the process concept under the design phase as well as the existing process plant

Renewable energy sources from biomass through incineration

The new five-fuel policy proposed by the Economic Planning Unit of the Malaysian Prime Minister’s Department, targets to achieve 5% electricity production from renewable energy sources to complement the current four-fuel policy of natural gas, coal, petroleum and hydroelectricity. Of particular interest are rice husk and palm wastes (fibre, shell and empty fruit bunch) with annual generation rates of 0.47 million tonnes (as of 2001) and 18.8 million tonnes(as of 2001)respectively. Apart from solving its disposal problems, energy recovery through combustion of rice husk results in the formation of ash that has high commercial value due to its high silica content. Palm wastes, on the other hand, are produced in quantities exceeding the internal energy requirements for palm oil mills. Realising the good potential of the fluidised bed technology in recovering energy from biomass, extensive research in the combustion of biomass using the fluidised bed technology is currently being carried out at Universiti Teknologi Malaysia(UTM). Different variants of the fluidised bed technology, namely the conventional bubbling fluidised bed, spouted bed(SB) and spinning fluidised bed(SFB) are being explored with the focus on the combustion of rice husk and palm wastes. This paper presents some of the results achieved from the research programmes

Understanding selected trace elements behavior in a coal-fired power plant in Malaysia for assessment of abatement technologies

The Proposed New Environmental Quality (Clean Air) Regulation 201X (Draft), which replaces the Malaysia Environmental Quality (Clean Air) 1978, specifies limits to additional pollutants from power generation using fossil fuel. The new pollutants include Hg, HCl, and HF with limits of 0.03, 100, and 15 mg/N-m3 at 6% O2, respectively. These pollutants are normally present in very small concentrations (known as trace elements [TEs]), and hence are often neglected in environmental air quality monitoring in Malaysia. Following the enactment of the new regulation, it is now imperative to understand the TEs behavior and to assess the capability of the existing abatement technologies to comply with the new emission limits. This paper presents the comparison of TEs behavior of the most volatile (Hg, Cl, F) and less volatile (As, Be, Cd, Cr, Ni, Se, Pb) elements in subbituminous and bituminous coal and coal combustion products (CCP) (i.e., fly ash and bottom ash) from separate firing of subbituminous and bituminous coal in a coal-fired power plant in Malaysia. The effect of air pollution control devices configuration in removal of TEs was also investigated to evaluate the effectiveness of abatement technologies used in the plant. This study showed that subbituminous and bituminous coals and their CCPs have different TEs behavior. It is speculated that ash content could be a factor for such diverse behavior. In addition, the type of coal and the concentrations of TEs in feed coal were to some extent influenced by the emission of TEs in flue gas. The electrostatic precipitator (ESP) and seawater flue gas desulfurization (FGD) used in the studied coal-fired power plant were found effective in removing TEs in particulate and vapor form, respectively, as well as complying with the new specified emission limits.Coals used by power plants in Peninsular Malaysia come from the same supplier (Tenaga Nasional Berhad Fuel Services), which is a subsidiary of the Malaysia electricity provider (Tenaga Nasional Berhad). Therefore, this study on trace elements behavior in a coal-fired power plant in Malaysia could represent emission from other plants in Peninsular Malaysia. By adhering to the current coal specifications and installation of electrostatic precipitator (ESP) and flue gas desulfurization, the plants could comply with the limits specified in the Malaysian Department of Environment (DOE) Scheduled Waste Guideline for bottom ash and fly ash and the Proposed New Environmental Quality (Clean Air) Regulation 201X (Draft)

Measurement of PCDD/Fs emissions from a coal-fired power plant in Malaysia and establishment of emission factors

This paper presents the PCDD/Fs emissions measured from a coal-fired power plant in Malaysia. The study discusses partitioning of PCDD/Fs in particle and gas phase, effects of coal quality to PCDD/Fs formation, effects of air pollution control device (APCD) configuration to PCDD/Fs formation and establishment of emission factors of PCDD/Fs from the studied coal-fired power plant. The results presented in this study were mostly in good agreement with the previous works on PCDD/Fs emissions conducted in other countries. Laboratory analysis results showed that PCDFs were the dominant congeners. The emissions of PCDD/Fs were low which most probably due to the high combustion efficiency. The PCDFs/PCDDs ratio was more than 1 and PCDD/Fs were detected in fly ash, hence speculating that the formation of PCDD/Fs during coal combustion was mainly through de novo synthesis. Analysis on partitioning of PCDD/Fs showed that the compounds were mainly emitted in gas phase. This study also indicated that type of coal influenced the formation of PCDD/Fs during coal combustion where bituminous coal with high sulfur (S) content resulted in slightly lower PCDD/Fs emissions compared to sub-bituminous coal. It was also found that operation of flue gas desulfurization (FGD) reduced the emission of PCDD/Fs. The established emission factors for PCDD/Fs were in the range of 0.08 to 0.11 ng I-TEQ/k